transition zone stellate fiber system

cellstructuremech:transition_zone_stellate_fiber_system · Cytoskeleton · Other · Proposed

A centrin-containing system of luminal fibers forming a nine-pointed stellate array attached to the outer microtubule doublets of the Chlamydomonas ciliary transition zone. It is distinct from the peripheral Y-links and from the central cylinder around which the fibers extend. [DOI:10.1083/jcb.124.5.795]

Image (not hosted — CC_BY_NC_SA_4_0): PMC2119956.1 Figure 2

Figure 2: Chlamydomonas transition zones in detergent-extracted models before (A-C) and after (D-F) calcium challenge. Cross-sections C and F contrast extended and condensed stellate fibers with displaced doublets. Source scale bar: 0.2 micrometers. TEM · Chlamydomonas reinhardtii (NCBITaxon:3055) · M. A. Sanders and J. L. Salisbury, Figure 2, Journal of Cell Biology 124 (1994), doi:10.1083/jcb.124.5.795, via PubMed Central; CC BY-NC-SA 4.0. Link only; no repository copy or adaptation. · CC_BY_NC_SA_4_0 · source: PMC PMC2119956.1 Figure 2 · DOI:10.1083/jcb.124.5.795

Synonyms: transition zone stellate fibers; transition region stellate fibers; stellate structure

Part of: ciliary transition zone (GO:0035869)

UniProt location names: UniProt Consortium, CC BY 4.0. Reference label and route sources.

Components

Component	Type	Part of / acts on	Grounding	Genes	Stoichiometry	Essential	Role
Stellate fiber centrins	Protein	part of	Reviewed label only (reviewed name; no accession asserted)			UNKNOWN	Calcium-binding constituents of the stellate fibers; centrin sequence mutations affect ordered transition-region assembly in Chlamydomonas. `DOI:10.1083/jcb.124.5.795` Results describe the centrin-based stellate fibers and antibody perturbations. `DOI:10.1083/jcb.119.6.1613` Transition-region structures are disrupted by E101K centrin and restored in intragenic revertants; the mutation is not specific to this fiber system.

Organism-specific protein examples

Named proteins in which each component's role was established, with the organism the evidence comes from. The component above is the taxon-agnostic family; these are the specific entries behind it.

Stellate fiber centrins

Accession	Protein	Gene	Organism	Entry
`UniProtKB:P05434`	Caltractin		Chlamydomonas reinhardtii (`NCBITaxon:3055`)	REVIEWED
Role and evidence (2 references) Species-level centrin example shared with other centrin assemblies, not a stellate-specific paralogue. `UniProtKB:P05434` Authority verifies the reviewed entry, recommended name and organism; no primary gene symbol is supplied. `DOI:10.1083/jcb.119.6.1613` The centrin/caltractin sequence, pCaBP4 clone and sequence-source citations identify the studied protein. vfl2 and intragenic revertants alter centrin assemblies.

Canonical examples

NCBITaxon:3055 Chlamydomonas reinhardtii — Methods use wild-type 137c and vfl2 isolate 416. Species identity was checked at NCBI; no culture-collection accession is inferred from these strain names. [DOI:10.1083/jcb.124.5.795]

Functions

calcium-induced doublet repositioning — Stellate-fiber contraction draws transition-zone doublets inward in detergent-extracted Chlamydomonas cell models. This bounded mechanical response does not establish universal necessity for flagellar excision.
- DOI:10.1083/jcb.124.5.795 Figure 2 compares extended and contracted arrays before and after calcium challenge.

Mechanism graphs

Calcium-induced stellate contraction in extracted Chlamydomonas models (FUNCTION)

Composition and attachment context accompany the observed contraction-to-doublet-displacement mechanism.

Subject	Predicate	Object	Evidence
Stellate fiber centrins	are constituents of	Transition-zone stellate fiber array	`DOI:10.1083/jcb.124.5.795` Centrin-based fiber identity and perturbation experiments.
Transition-zone stellate fiber array	attaches to	Outer microtubule doublets	`DOI:10.1126/science.abm6704` Native cryo-ET resolves attachment at protofilament A3.
Calcium challenge of detergent-extracted models	triggers	Stellate-fiber contraction	`DOI:10.1083/jcb.124.5.795` Results and Figure 2 before/after comparison.
Transition-zone stellate fiber array	undergoes	Stellate-fiber contraction	`DOI:10.1083/jcb.124.5.795` Figure 2D-F and accompanying Results.
Stellate-fiber contraction	draws doublets into	Inward displacement of doublets	`DOI:10.1083/jcb.124.5.795` Figure 2C/F and accompanying mechanical interpretation.

Discussions

CURATION_TODO (RESOLVED): Separate luminal stellate fibers from neighboring transition-zone structures. Shared location or centrin does not imply identical structures.
CURATION_TODO (OPEN): Resolve preparation-dependent contributions of stellate contraction to flagellar excision. Published results disagree, and the perturbations affect multiple assemblies.
CURATION_TODO (OPEN): Resolve exact centrin-family grounding and the remaining molecular inventory. One identified constituent does not establish molecular sufficiency, stoichiometry or universal assembly essentiality.
CURATION_TODO (RESOLVED): Do not import whole-transition-zone or severing proteins as stellate constituents. Region-level enrichment and enzymatic activity are not fiber-specific localization.
CURATION_TODO (OPEN): Extend directly demonstrated taxonomic scope and resolve an exact function term. A canonical species does not establish a prevalence statement for an entire clade.

Evidence

DOI:10.1083/jcb.124.5.795 Full primary PDF text read; Figure 2 and Table I visually inspected. Physical response is distinguished from disputed excision necessity.
DOI:10.1083/jcb.119.6.1613 Primary Methods, mutant/revertant Results and Table II inspected; centrin assembly evidence is pleiotropic.
DOI:10.1242/jcs.99.4.731 Complete publisher abstract read; full text is access-restricted and figures remain unread. Reports autotomy without organized stellate fibers or detectable narrowing.
DOI:10.1091/mbc.9.5.1195 Primary Introduction, Methods, Results and Discussion read at PMC25341; figures uninspected. Katanin experiments do not identify stellate-fiber constituents.
DOI:10.1016/j.cub.2014.11.066 Primary ultrastructure Results read: isolated central cylinders persist after stellate fibers are no longer identifiable.
DOI:10.1126/science.abm6704 Published primary architecture Results and Figure 1 caption read from the institutional PDF. Native cryo-ET distinguishes luminal stellates, Y-links and the distal microtubule sleeve; figures not visually inspected.
GO:0043232 Verified intracellular membraneless organelle as a broad is-a parent.
GO:0035869 Verified ciliary transition zone as the enclosing region, not exact identity.

Curation history

2026-10-04T04:58:00Z codex · CREATED_RECORD — Scaffolded by scripts/new_record.py
2026-10-04T04:59:12Z codex · EXPANDED_RECORD — Added stellate-fiber identity and parthood, verified centrin example, canonical species, bounded contraction mechanism, explicit conflicting excision evidence, component exclusions and a link-only micrograph.

Source: data/structures/cytoskeleton/transition_zone_stellate_fiber_system.yaml